This invention relates to a two-needle overedge sewing machine and more particularly to a guiding device for a thread chain formed extending from the fabric material when an overedge sewing operation is finished.
When an overedge sewing operation performed by a conventional overedge sewing machine is finished, a thread chain is formed that extends from the fabric material. Where a two-needle overedge sewing machine is used, after each completion of the overedge sewing process, the thread chain is enfolded or back tacked between the fabric material and the looper threads to prevent the beginning or starting edge of the fabric material from fraying. Such an enfolding or back tacking process is well-known to those of skill in the art.
Referring to FIG. 7, it is a well-known practice to provide an inner chain-off finger 2 at the throat plate in a conventional overedge sewing machine to prevent the fabric material from sinking or dropping stitches by the two needles, to prevent the skipping of stitches, and to make sure the fabric has a good hand or feel.
Referring again to FIG. 7, numeral 1 denotes a throat plate and numeral 2 denotes an inner chain-off finger. Numeral 3 denotes an outer chain-off finger and numeral 4 denotes a needle entry by the right needle 11R. Numeral 5 denotes a thread chain and numeral 6 denotes a work fabric in which the thread chain is enfolded or back tacked between the work fabric 6 and the looper thread. Numeral 7 denotes a thread-chain-holding-and-cutting device which holds the thread chain and cuts it. Numeral 11L denotes a left needle.
How the thread chain is enfolded or back tacked between the fabric material and the looper thread will now be explained hereinafter. When one overedge sewing operation is finished, the presser foot (not shown) will be lifted by pedal action and the thread chain 5 is pulled in the direction of feeding to release the needle thread twining around the inner chain-off finger 2 and the outer chain-off finger 3. Then, the fabric material 6 is turned back or rotated counter clockwise to the operator's side, the thread chain 5 is inserted into the thread-chain-holding-and-cutting device 7, and the thread chain 5 is clamp-cut. New fabric material is set with the presser foot in a processing condition and the stitching starts. The thread chain is enfolded or back tacked into the seam of the new fabric material. If the thread chain 5 hangs at the inner chain-off finger 2, the thread chain is stitched by the needle, and in such a case, the thread chain would not be enfolded or back tacked.
Referring to FIG. 8A, and FIG. 8B, an application (application number 60-143591) previously filed in Japan as "Thread Chain Sewing Method and Device for Two-Needle Overlock Sewing Machine" now Japanese Patent No. 62-005387, the same applicant (Tokyo Juki Industrial Co., Ltd.) will be explained hereafter. FIG. 8A. is a front view and FIG. 8B is a plan view drawing. Numeral 10R denotes a right needle thread which is thread to the right needle 11R and numeral 10L denotes a needle thread which is threaded to the left needle 11L. Numeral 12 denotes a lower looper, numeral 13 denotes a needle thread restricting device and provides a thread restrictor 13a at its free end. When the thread chain which is twining around the inner chain-off finger 2 and the outer chain-off finger 3 is pulled in the direction of feeding, the restrictor 13a prevents the needle threads 10R, 10L from sliding in the direction of arrow "B" along the sloped arm of the lower looper 12. Thus, when the thread chain is rotated counter clockwise to the operator's side, the needle threads 10R, 10L will not hang at the inner chain-off finger 2.
According to the above-mentioned application, longer needle thread 10 is drawn per each stitch because the restrictor 13a tends to push the needle thread further rightward as shown in FIG. 9B. Comparing FIG. 9B with FIG. 9A, which has no restrictor 13a, it is apparent that FIG. 9B draws more thread than FIG. 9A per each stroke of the lower looper. Thereby, to adjust the supply of needle thread, the standard thread take-up assembly has to be redesigned and the needle thread tension must be adjusted also. Where the stop position of the lower looper 12 is changed because the motor clutch was worn out, or any other reason, and is changed to left side slightly. Therefore, the soft chain is apt to be hung at the inner chain-off finger 2 when it is rotated counter clockwise to the operator's side.